Senior Capstone Research Paper

Meta-Analysis of Triclosan

Brandon E. Rawlinson

April 29th, 2013

Abstract

                  Triclosan is a popular and pervasive anti-bacterial agent.  It eliminates bacteria using a similar mechanism as many antibiotics.  Triclosan can produce antibiotic cross-resistant strains of bacteria.  Trace amounts of triclosan are prevalent in the water supply and it acts as an endocrine disruptor in animals and plants.  I utilized Google Scholar to conduct an analysis on the adverse effects of triclosan. I researched the current movement to ban triclosan in media and political outlets. I learned that both sides of the debate are clearly biased. There is insufficient evidence to support that triclosan significantly contributes to antibiotic cross-resistance in bacteria.  However, triclosan has a powerful ability to eradicate biofilms in water environments. Steps should be taken to regulate triclosan, but a blanket ban is unnecessary.

Introduction

Over the past one hundred years scientists have discovered and engineered antibiotics, anti-microbial agents, and vaccines in response to the discovery of pathogens.  Products containing chemicals such as lye, ethanol, bleach, triclosan, and hydrogen peroxide are manufactured and distributed across the globe to help individuals and institutions defend against the vast array of pathogenic microorganisms.

The anti-microbial agent Triclosan was developed by Ciba and emerged in hospitals in the 1970s.  Triclosan is a phenyl-ether that is recognized by the FDA as a Class III drug and a pesticide by the EPA (APUA, 2011). Triclosan targets gram-positive and gram-negative non-sporulating bacteria and some fungi. Triclosan is bactericidal at high concentrations and bacteriostatic at lower concentrations and is used in a wide variety of products including: toothpaste, clothing, toys, computer equipment, hand soaps, and toothpaste (Glaser, 2004).  Infusion of triclosan in products that are not classified as cleaning agents, such as cutting boards or plastics, is largely scientifically unsupported (Glaser, 2004). However when used in detergents and hand soaps, triclosan is most effective against Staphylococci, Streptococci, mycobacteria and E. coli by blocking the active site of the enoyl-acyl carrier protein reductase enzyme (ENR) used in fatty-acid synthesis, thereby rendering the cell unable to replicate.  Humans do not have ENR and therefore triclosan is generally considered safe for human contact (APUA, 2011).

Due to the widespread use of triclosan, studies have shown that it has penetrated the water supply and has been found in precarious places such as human breast milk (Adolfsson-Erici, Pettersson, Parkkonen, & Sturve, 2002). The purpose of this study was to determine the effects of triclosan on the environment, particularly as a hormone disruptor, its potential evolutionary role in developing bacterial resistance and cross-resistance with antibiotics, its discussion, representation, and perception by media sources, and its political implications.

Scholarly Review

                  In order to determine the anthropogenic effects of triclosan based on scientific literature I utilized the online search engine Google Scholar.  I entered the key words “triclosan AND effects”, “triclosan AND resistance”.  I also utilized any relevant sources referenced in my findings.  I placed all reference material into two categories: “”studies related to environmental effects” and “studies related to bacterial resistance”.   I only excluded studies that were incomplete in identifying a direct link between triclosan and its hypothesized effects. Additionally, I selected studies that were able to identify a specific method of bacterial resistance employed by the bacterium. When selecting studies for hormonal disruption, I chose those that were able to successfully identify the minimum amount required to elicit a response in the organism and identify the specific outcome of triclosan presence. There is the possibility that some studies were omitted due to insufficient expertise on the subject on my part.  Overall, I was able to compile a fair sample-size of studies that support the hypothesis that triclosan acts as a hormone disruptor and that it can produce bacterial cross-resistance with antibiotics. I constructed two tables in order to summarize my findings.

Table 1: Summary of the effects of triclosan on various frog, fish, plant, and mammal species.

Organism	Effect	Min. Concentration	Reference
Rana catesbeiana	Modulates thyroid hormone gene expression, disrupts postembryonic development	0.3 μg/L	Veldhoen et al. 2006
Xenopus laevis	No significant effect on thryoid was measured	1.5-32.5 μg/L	Fort et al. 2009
Gambusia affinis	Induces vitellogenin, reduces sperm count	29 μg/L	Raut and Angus 2010
Danio rerio	High toxicity in embryo/larvae, delays hatching and development	0.42 mg/l	Oliveira et al. 2009
Pimephales promelas	Impairs swimming behavior, alters excitation-contraction gene expression	75 μg/L	Fritsch et al. 2013
Oryzias latipes	High toxicity in early life stages, weakly estrogenic, induces vitellogenin in males	1 mg/l, 1 μg/l	Ishibashi et al. 2003
Oryzias latipes	Changes in fin length, lethal at high concentrations, no effect on sex-ratio	1 mg/l, 1 μg/l	Foran et al. 2000
Sesbania herbacea	Decreases seed germination, root length and root surface area	0.05-10.0 ppb	Stevens et al. 2010
Bidens frondosa	Decreases seed germination, root length and root surface area	0.05-10.0 ppb	Stevens et al. 2010
Eclipta prostrata	Decreases root length and surface area	0.05-10.0 ppb	Stevens et al. 2010
Chlamydomonas	Decreases total algal biomass	0.12 μg/L	Wilson et al. 2003
Scenedesmus	Decreases total algal biomass	0.12 μg/L	Wilson et al. 2003
Oryza sativa	Inhibits root elongation, decreases shoot height and root length	1 mg/kg	Liu et al. 2009
Cucumis sativus	Inhibits root elongation, decreases shoot height and root length	1 mg/kg	Liu et al. 2009
Rattus norvegicus	Increases liver weight, decreases thyroxine levels (T4)	100 mg/kg	Crofton et al. 2007
Rattus norvegicus	decreases testosterone, thryoxine (T4), and triiodothyronine (T3).	30 mg/kg, 200 mg/kg	Zorilla et al. 2008
Rattus norvegicus	Enhances uterotrophic response	4.69 mg/kg	Louis et al. 2013

Effects of triclosan on plant and algae species

                  When triclosan is present in the water supply at concentrations exceeding 0.05 ppb it will negatively affect aquatic plants. In two species of aquatic plants, Bidens frondosa and Sesbania herbacea, the rate of seed germination, length of roots and total root surface area were significantly decreased (Stevens, Kim, Adhikari, Vadapalli, & Venables, 2009).  A third species of aquatic plant within the same study, Ecplita prostrate only demonstrated a decrease in root length and surface area to a significant degree (Stevens, Kim, Adhikari, Vadapalli, & Venables, 2009).   Furthermore, triclosan inhibits root elongation and decreases shoot height and root length in rice (Oryza sativa) and cucumber (Cucumis sativus) plants (Liua, Yinga, Yanga, & Zhoub, 2009).  In areas that are downstream from wastewater treatment plants, where triclosan usually enters the water supply, levels above 0.12 μg/L contributed to a decrease in total algal biomass, but not in specific algae function (Wilson, Smith, deNoyelles, & Larive, 2003).  Overall, this sample of studies acts as a strong indicator that the current levels of triclosan in the water supply have an effect on plant ecology.

Effects of triclosan on fish

                  Triclosan is highly toxic to fish species Donio rerio (Oliveira, Domingues, Grisolia, & Soares, 2009) and Oryzias Latipies Ishibashi et al. 2003) at concentractions around 1 mg/L.  In Gambusia affinis, Oryzias Latipes, triclosan acted as an endocrine disruptor by inducing vitellogen (egg development) in males, but did not show any effect on population sex-ratio, notwithstanding, in the latter species, it showed weak estrogenic effects.  Triclosan also directly impaired swimming behavior and altered excitation-contraction coupling gene expression in Pimephales promias (Fritsch, et al., 2013).  This sample of studies on the effects of triclosan on fish physiology show that triclosan in the water supply can have a significant effect on development, morphology, and behavior.

Effects of triclosan on frogs and rats

                  The North American Bullfrog (Rana catesbeiana) showed significant modulation in thyroid hormone gene expression and disruption in postembryonic development at 0.3 μg/L (Veldhoen, et al., 2006).  However, a related follow-up study conducted at Oklahoma State University by Fort et al. in 2009 on the Xenopus laevis indicated no significant effect on thyroid hormone production.  Fort et al. attributed the discrepancy to measuring for thyroid levels at different stages in development and with different species of frog. However, it must be carefully noted that Ciba, the proprietor of triclosan in North America, provided the majority of funding for the Fort study. Additional analysis of their study should be conducted, in addition to further research on the effects of triclosan on frog thyroid hormone management.

                  Triclosan also exhibited effects on thyroid hormones in rats. Triclosan decreased T4 (Crofton, Paul, DeVito, & Hedge, 2007) T3, and testosterone levels (Zorrilla, et al., 2008) in Rattus norvegicus. Furthermore, Louis et al. (2013) demonstrated that triclosan presence in this species of rat enhanced the uterotrophic response including measured epithelial growth in the reproductive tract. It should be noted that this was a secondary effect; triclosan acted in concert with estrogen to produce these results. Excluding the Fort study, the sample of studies selected supports the hypothesis that triclosan will act as a hormone disruptor at particular concentrations in mammals and frogs.

Table 2: Summary of Triclosan-induced bacterial resistance

Study	Bacteria	Role of Triclosan in Antibiotic Resistance Development
McMurray et al. (1998)	Escherichia coli	encourages preferential survival of resistant mutants
McBain et al. (2003)	Multiple bacterial strains	does not affect antimicrobial susceptibility
Oggioni et al. (2013)	Multiple bacterial strains	no conclusive evidence of significant resistance development
Russell (2004)	Multiple bacterial strains	no conclusive evidence of significant resistance development
Lamber (2004)	Pseudomonas aeruginosa	no conclusive evidence of significant resistance development
Chaunchuen et al. (2002)	Pseudomonas aeruginosa	selects for first part of two-part efflux pump system
Birosova and Mikulasova (2008)	Salmonella enterica	selects for strains with increased antibiotic MIC
Suller and Russell (2000)	Staphylococcus aureus	no antibiotic resistance observed
Lambert (2004)	Staphylococcus aureus	no conclusive evidence of significant resistance development
Tkachenko et al. (2007)	Staphylococcus aureus	selects for strains that sequester biocide/antibiotic molecule in membrane
Sanchez et al, (2005)	Stenotrophomonas maltophilia	selects for strains that overproduce efflux pump

Triclosan-induced bacterial cross-resistance

                  Triclosan functions similar to some antibiotics in its ability and mechanism to defeat microorganisms.  In nature resistant strains of bacteria can develop. The most alarming potentiality is that the triclosan-resistant strains could produce cross-resistant strains for antibiotics. The study sample I selected gives mixed opinions on the role of triclosan in significantly selecting for bacterial cross-resistance.  Only in the most recent study published did triclosan select for strains that were significantly resistant in Staphyloccocus aureus by which the cells successfully sequestered the molecule in the membrane (Tkachenkoa, et al., 2007). This study also examined the potential for cross-resistance development via this same mechanism and concluded that the bacteria also established resistance to ciprofloxacin, an antibiotic. Triclosan also played a role in potential cross-resistance development in Pseudomonas aeruginosa where the researchers discovered the efflux pump used to defend against triclosan is also used in a similar efflux pump system of strains resistant to antibiotics.  In this case, the antibiotic resistant strains had one additional pump regulated by an upstream gene. Researchers concluded that triclosan resistance could easily contribute to antibiotic resistance if a simple mutation occurred at that gene (Chuanchuen, Narasaki, & Schweizer, 2002).  However, a later study conducted by Lambert (2004) concluded that the hypothesized cross-resistance development was not likely in the wild and was not supported by observation in nature.  Recently, researchers met in Lisbon, Portugal to discuss the role biocides, such as triclosan, have in developing antibiotic cross-resistance and decided that there was “no conclusive evidence that [biocide resistance] also determined or will determine an increase in antibiotic resistance (Oggioni, Furi, Coelho, Maillard, & Martinez, 2013).”

Media Critique

I performed a Google search using the keyword “Triclosan” and quickly found multiple media outlets discussing the current issue.  Most media sources fall into two categories that follow separate trends. The first article representative of one category is entitled “Coming Clean on Triclosan” by Diedre Imus (2011).  The article is in favor of controlling or even banning triclosan. The author lists the various products that contain triclosan and then cites the CDC finding trace samples of the substance across the nation’s water supply.  Before telling the reader what to do next, the author outlines the United States’ inability to keep up with Europe in regulating the triclosan.  This article is largely biased, and cherry-picks scientific literature to support its opinion.  Imus even employs the use of scare tactics by citing a rare process wherein triclosan can become chloroform upon contact with sunlight.

                  Another approach to discussing triclosan in the media is represented by an article that appeared on the political news website RealClearPolicy in 2012.  In this article Paul Alexander describes his journey of investigating triclosan. He describes its origins and use, and then finishes the article discussing the FDA’s continued inability to reach a consensus on banning the substance. He concludes that both the EPA and FDA are not going to make a clear policy decision on the substance because they do not feel it is dangerous, but want to avoid the harassment of environmental groups. In exemplary form, Alexander then moves to discuss the power of triclosan to rid the earth of such abominable bacterial infections such as the plague.  The author does not utilize any primary scientific sources to support any of the claims he makes and does not attempt to present both sides of the argument clearly (Alexander, 2012).

                  Based on my sample of the media coverage of the topic of triclosan, it is evident that the media is underpowered by scientific literature when attempting to present any form of objectivity. For the most part it is obvious in many articles that the media source is completely biased and emotionally charges the article in order to elicit a populous response.

The Politics

                  Currently, triclosan is not banned in the U.S. However, companies like Johnson & Johnson and Colgate-Palmolive have voluntarily phased out its use in a number of household products (Glaser, 2004).  In the state of Minnesota a ban was introduced to a senate committee, discussed amongst representatives of both sides, and promptly turned down in less than two days. Lawmakers said that the ban was unable to pass because a complete ban did not make sense considering the benefits of triclosan as an anti-microbial agent.  In a news article covering the proposed legislation, Brian Sansoni, who was identified as an “institute vice president”, made several claims and points in defense of triclosan during the debate (Dunbar, 2013). I researched this individual and found him to be the Vice President of the American Cleaning Institute. Furthermore, I investigated the members listed on the website and found a large group of chemical companies including Microban International, a manufacturer of triclosan-infused plastics. The website of the American Cleaning institute has an entire page devoted to studies supporting triclosan. Most of the peer-reviewed studies cited on the website conclude that there is no convincing evidence that triclosan causes cross-resistance in antibiotics.  There are no sources or links depicting the hypothesized negative consequences of triclosan in the environment as an endocrine disruptor (American Cleaning Institute, 2013).

                  Conversely, the websites operated by those supporting triclosan regulation present the information in a less biased method, but not completely free of partiality. Beyondpesticides.org is major source of information on this topic. Their website clearly states information based on peer-reviewed studies and offers direct links to the journal articles and citations. However, this website does not provide any links to studies that have rejected the hypothesis for cross-resistance on the basis of insignificant examples in nature. Additionally, the organizations that support a ban on triclosan fail to provide any data regarding the actual levels of triclosan in waterways and compare those to the minimal concentrations required to elicit a response in organisms. There is also the lack of any studies presented describing the confirmed effectiveness of wastewater plants in removing triclosan from the water supply.

Recommendations and conclusions

                  Solely based on the current library of knowledge concerning triclosan, it is difficult to fully support a complete ban on its usage. An array of studies show the potentiality of cross-resistance developed from triclosan, but there are few, if any, showing this actually occurring naturally.  This is most likely because cross-resistant strains are less fit than their brothers.  In regards to triclosan as an ecological disruptor there is significant evidence that it is affecting biomass of aquatic plants. However, these studies mention that triclosan must act in concert with numerous other agents to have a significant effect.  In water sources that undergo heavy usage, triclosan has been shown to reach concentration levels high enough to eradicate biofilms. This in turn affects the aquatic ecology as algae growth was significantly inhibited (Ricart, et al., 2010).  For the most part, however, trace levels of triclosan are found in rivers and streams across the United States, but most studies have measured these concentrations at levels below environmentally relevant concentrations (Hua, Bennett, & Letcher, 2005).  Finally, most triclosan molecules enter the environment after passing through wastewater treatment plants and research suggests that there are microorganisms that efficiently degrade the molecule (Federle, Kaiser, & Nuck, 2009).

                  At this point, evidence suggests that triclosan has potential to become a hazard in the environment. When considering the risks and benefits, especially in comparison to soap and water, it would be a sound policy maneuver to regulate triclosan and promote alternative antimicrobial agents. I would suggest regulators work to keep triclosan in medical institutions and out of household objects and usage.  By minimizing the prevalence of triclosan, the environmental and evolutionary hazards can hopefully be averted.

References

Adolfsson-Erici, M., Pettersson, M., Parkkonen, J., & Sturve, J. (2002). Triclosan, a commonly used bacteriocide found in human milk and in the aquatic environment in Sweden. Chemosphere, 1485-1489.

Alexander, P. (2012, November 29). The Dysfunctional Politics of Hand Soap. Retrieved April 21, 2013, from RealClearPolicy: http://www.realclearpolicy.com/articles/2012/11/29/the_dysfunctional_politics_of_hand_soap_359.html

American Cleaning Institute. (2013). Antimicrobials and Antibacterial Information. Retrieved April 25, 2013, from http://www.cleaninginstitute.org/antibacterials/

APUA. (2011, January). Triclosan. Boston, MA. Retrieved April 1, 2013, from White Paper on Triclosan: http://www.tufts.edu/med/apua/consumers/personal_home_21_4240495089.pdf

Birosova, L., & Mikulasova, M. (2009). Development of triclosan and antibiotic resistance in Salmonella enterica serovar Typhimurium. J Med Microbiol, 436-441.

Chuanchuen, R., Narasaki, C. T., & Schweizer, H. P. (2002). The MexJK Efflux Pump of Pseudomonas aeruginosa Requires OprM for Antibiotic Efflux but Not for Efflux of Triclosan. Journal of Bacteriology, 5036-5044.

Ciusaa, M. L., Furia, L., Knight, D., Decorosic, F., Fondid, M., Raggie, C., et al. (2012). A novel resistance mechanism to triclosan that suggests horizontal gene transfer and demonstrates a potential selective pressure for reduced biocide susceptibility in clinical strains of Staphylococcus aureus. International Journal of Antimicrobial Agents, 210-220.

Crofton, K. M., Paul, K. B., DeVito, M. J., & Hedge, J. M. (2007). Short-term in vivo exposure to the water contaminant triclosan: Evidence for disruption of thyroxine. Environmental Toxicology and Pharmacology, 194-197.

Dunbar, E. (2013, March 12). Lawmakers consider banning triclosan, other chemicals. MPRNews. St. Paul, MN.

Federle, T. W., Kaiser, S. K., & Nuck, B. A. (2009, November). Fate and effects of triclosan in activated sludge. Environmental Toxicology and Chemistry, 1330-1337.

Foran, C., Bennett, E., & Benson, E. (2000). Developmental evaluation of a potential non-steroidal estrogen: triclosan. Marine Environmental Research, 153-156.

Fort, D. J., Rogers, R. L., Gorsuch, J. W., Navarro, L. T., Peter, R., & Plautz, J. R. (2009). Triclosan and Anuran Metamorphosis: No Effect on Thyroid-Mediated Metamorphosis in Xenopus laevis. Toxicological Sciences, 392-400.

Fritsch, E. B., Connon, R. E., Werner, I., Davies, R. E., Beggel, S., Feng, W., et al. (2013). Triclosan Impairs Swimming Behavior and Alters Expression of Excitation-Contraction Coupling Proteins in Fathead Minnow (Pimephales promelas). Environmental Science and Technology, 2008-2017.

Glaser, A. (2004). The Ubiquitous Triclosan. Pesticides and You, 12-17.

Hua, W., Bennett, E. R., & Letcher, R. J. (2005). Triclosan in waste and surface waters from the upper Detroit River by liquid chromatography-electrospray-tandem quadrupole mass spectrometry. Environmental International, 621-630.

Imus, D. (2011, January 26). Coming Clean on Triclosan. Retrieved April 21, 2013, from Foxnews.com: http://www.foxnews.com/health/2011/01/26/coming-clean-triclosan/

Lambert, R. (2004). Comparative analysis of antibiotic and antimicrobial biocide susceptibility data in clinical isolates of methicillin-sensitive Staphylococcus aureus, methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa between 1989 and 2000. Journal of Applied Microbiology, 1365-2672.

Leea, D. G., Zhaoa, F., Rezenomb, Y. H., Russell, D. H., & Chu, K.-H. (2012). Biodegradation of triclosan by a wastewater microorganism. Water Research, 4226-4234.

Liua, F., Yinga, G.-G., Yanga, L.-H., & Zhoub, Q.-X. (2009). Terrestrial ecotoxicological effects of the antimicrobial agent triclosan. Ectoxicology and Environmental Safety, 86-92.

Louis, G. W., Hallinger, D. R., & Stoker, T. E. (2013). The effect of triclosan on the uterotrophic response to extended doses of ethinyl estradiol in the weanling rat. Reproductive Toxicology, 71-77.

McBain, A. J., Bartolo, R. G., Catrenich, C. E., Charbonneau, D., Ledder, R. G., Price, B. B., et al. (2013). Exposure of Sink Drain Microcosms to Triclosan: Population Dynamics and Antimicrobial Susceptibility. Applied and Environmental Microbiology, 5433-5442.

McMurray, L. M., Oethinger, M., & Levy, S. B. (1998). Overexpression of marA, soxS, or acrAB produces resistance to triclosan in laboratory and clinical strains of Escherichia coli. FEMS Microbiology Letters, 305-309.

Oggioni, M. R., Furi, L., Coelho, J., Maillard, J.-Y., & Martinez, J. L. (2013). Recent advances in the potential interconnection between antimicrobial resistance to biocides and antibiotics. Lisbon: Expert Reivew of Anti-infective Therapy.

Oliveira, R., Domingues, I., Grisolia, C. K., & Soares, A. M. (2009). Effects of triclosan on zebrafish early-life stages and adults. Environmental Science and Pollution Research, 679-688.

Rhaul Oliveira, I. D., Oliveira, R., Domingues, I., Grisolia, C. K., & Soares, A. M. (2009). Effects of triclosan on zebrafish early-life stages and adults. Environmental Science and Pollution Research, 679-688.

Ricart, M., Guasch, H., Alberch, M., Barcelo, D., Bonnienau, C., Geiszinger, A., et al. (2010). Triclosan persistence through wastewater treatment plants and its potential toxic effects on river biofilms. Aquatic Toxicology, 346-353.

Ricarta, M., Guasch, H., Alberch, M., Barceloa, D., Bonnienau, C., Geiszinger, A., et al. (2010). Triclosan persistence through wastewater treatment plants and its potential toxic effects on river biofilms. Aquatic Toxicology, 346-353.

Russell, A. (2004). Whither Triclosan? Journal of Antimicrobial Chemotherapy, 1-3.

Samiksha, R. A., & Angus, R. A. (2010). Triclosan has endocrine-disrupting effects in male western mosquitofish, Gambusia affinis. Environmental Toxicology and Chemistry, 1287-1291.

Sanchez, P., Moreno, E., & Martinez, J. L. (2005). The Biocide Triclosan Selects Stenotrophomonas maltophilia Mutants That Overproduce the SmeDEF Multidrug Efflux Pump. Antimicrobial Agents and Chemotherapy, 781-782.

Schweizer, H. P. (2001). Triclosan: a widely used biocide and its link to antibiotics. FEMS Microbiology Letters, 1-7.

Stevens, K. J., Kim, S.-Y., Adhikari, S., Vadapalli, V., & Venables, B. J. (2009). Effects of triclosan on seed germination and seedling development of three wetland plants: Sesbania herbacea, Eclipta prostrata, and Bidens frondosa†. Environmental Toxicology and Chemistry, 2589-2609.

Suller, M., & Russell, A. (2000). Triclosan and antibiotic resistance in Staphylococcus aureus. Journal of Antimicrobial Chemotherapy, 11-18.

Tkachenkoa, O., Sheparda, J., Aris, V. M., Joy, A., Bello, A., Londonoa, I., et al. (2007). A triclosan-ciprofloxacin cross-resistant mutant strain of Staphylococcus aureus displays an alteration in the expression of several cell membrane structural and functional genes. Research in Microbiology, 651-658.

Veldhoen, N., Skirrow, R. C., Osachoff, H., Wigmore, H., Clapson, D. J., Gunderson, M. P., et al. (2006). The bactericidal agent triclosan modulates thyroid hormone-associated gene expression and disrupts postembryonic anuran development. Aquatic Toxicology, 217-227.

Veldhoena, N., Skirrow, R. C., Osachoff, H., Wigmore, H., Clapson, D. J., Gunderson, M. P., et al. (2006). The bactericidal agent triclosan modulates thyroid hormone-associated gene expression and disrupts postembryonic anuran development. Aquatic Toxicology, 217-227.

Wilson, B. A., Smith, V. H., deNoyelles, F., & Larive, C. K. (2003). Effects of Three Pharmaceutical and Personal Care Products on Natural Freshwater Algal Assemblages. Enviornmental Science and Technology, 1713-1719.

Zorrilla, L. M., Gibson, E. K., Jeffay, S. C., Crofton, K. M., Setzer, W. R., Cooper, R. L., et al. (2008). The Effects of Triclosan on Puberty and Thyroid Hormones in Male Wistar Rats. Toxicological Sciences, 56-64.